package kata;

import java.util.Stack;

public class Calculator {
    private Stack<String> _operators;
    private Stack<Double> _operands;

    public Calculator() {
        _operators = new Stack<String>();
        _operands = new Stack<Double>();
    }

    public void operand(Double operand) {
        _operands.push(operand);
    }

    public void operator(String operator) {
        while (!_operators.isEmpty() && priority(_operators.peek()) >= priority(operator)){
            _operands.push(evaluate());
        }

        _operators.push(operator);
    }

    public void leftParenthesis() {
        _operators.push("(");
    }

    public void rigthParenthesis() {
        while (!_operators.peek().equals("(")) {
            _operands.push(evaluate());
        }
    }

    private Double evaluate() {
        String operator = _operators.pop();
        Double operandRight = _operands.pop();
        Double operandLeft = _operands.pop();
        Double evaluationResult = 0.0;

        switch (operator) {
            case "+":
                evaluationResult = operandLeft + operandRight;
                break;

            case "-":
                evaluationResult = operandLeft - operandRight;
                break;

            case "*":
                evaluationResult = operandLeft * operandRight;
                break;

            case "/":
                if (operandRight == 0.0) {
                    throw new IllegalArgumentException();
                }

                evaluationResult = operandLeft / operandRight;
                break;
        }

        return evaluationResult;
    }

    private int priority(String operator) {
        if (operator.equals("(") || operator.equals(")")) {
            return 0;
        }
        else if (operator.equals("^")) {
            return 4;
        }
        else if (operator.equals("*") || operator.equals("/")) {
            return 3;
        }
        else if (operator.equals("+") || operator.equals("-")) {
            return 2;
        }
        else {
            return 0;
        }
    }

    public Double pop() {
        return _operands.pop();
    }

    public void clear() {
        _operators.clear();
        _operands.clear();
    }
}